U.S. patent number 4,657,717 [Application Number 06/712,009] was granted by the patent office on 1987-04-14 for forming fibre-plastics composites.
This patent grant is currently assigned to Alcan International Limited. Invention is credited to Anthony J. Barnes, James B. Cattanach.
United States Patent |
4,657,717 |
Cattanach , et al. |
April 14, 1987 |
Forming fibre-plastics composites
Abstract
A plastics composite of fibres in a thermoformable matrix is
formed by contacting the composite with a sheet of metal and
deforming the metal plastically. The thermoformable matrix may be
thermoplastic or thermosetting and the metal may be superplastic.
The matrix may be deformed between the sheet and another sheet or
between the sheet and a mould. Thin bodies of complex shape may be
formed.
Inventors: |
Cattanach; James B.
(Middlesbrough, GB2), Barnes; Anthony J. (Malvern,
GB2) |
Assignee: |
Alcan International Limited
(Montreal, CA)
|
Family
ID: |
26287461 |
Appl.
No.: |
06/712,009 |
Filed: |
March 15, 1985 |
Foreign Application Priority Data
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Mar 16, 1984 [GB] |
|
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8406869 |
Nov 27, 1984 [GB] |
|
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8429906 |
|
Current U.S.
Class: |
264/102; 264/292;
264/316; 264/257; 264/258; 264/314; 264/324 |
Current CPC
Class: |
B29C
43/3642 (20130101); B29C 51/28 (20130101); B29C
70/42 (20130101); B29C 70/542 (20130101); B32B
15/08 (20130101); B32B 3/28 (20130101); B32B
7/12 (20130101); B29C 43/12 (20130101); B29C
2043/3644 (20130101); B32B 2305/076 (20130101); B29K
2705/00 (20130101); B29L 2009/00 (20130101); B32B
2309/68 (20130101); B29K 2105/06 (20130101) |
Current International
Class: |
B29C
51/28 (20060101); B29C 51/26 (20060101); B29C
43/36 (20060101); B32B 15/08 (20060101); B29C
70/04 (20060101); B29C 70/42 (20060101); B29C
70/54 (20060101); B29C 43/10 (20060101); B29C
43/12 (20060101); B29C 043/02 () |
Field of
Search: |
;264/316,257,275,1.9,102,258,292,314,324 ;249/94 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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535611 |
|
Apr 1941 |
|
GB |
|
1461317 |
|
Jan 1977 |
|
GB |
|
Primary Examiner: Lowe; James
Attorney, Agent or Firm: Browdy and Neimark
Claims
We claim:
1. A method of forming a three dimensional shaped article of a
plastics composite comprising superimposed layers of fibers
dispersed in a matrix of a thermoformable material, comprising the
steps of
providing a body of said composite to be reshaped and having a
first side and a second side;
contacting at least the first side of said body of said composite
with a sheet of a metal which is capable of being plastically
deformed at an elevated temperature,
clamping edges of said metal sheet to prevent movement of said
edges during subsequent deformation, and applying vacuum to remove
air from between said metal sheet and said body to bring the
composite body tightly against the metal sheet and to provide
support for said body;
bringing the metal sheet and the composite body to an elevated
temperature at which the metal sheet can be substantially
plastically deformed and at which the composite body can conform to
the plastically deformed shape of the metal sheet, and
applying fluid pressure to the metal sheet while the second side of
the composite body is at least partly reshaped by a mold so that
the metal sheet becomes substantially plastically deformed to a
relatively new deep shaped geometry and the first side of the
composite body is formed to the relatively deep shaped new geometry
by the plastic deformation of the metal sheet, including relative
movement of the fibers of the superimposed layers to accommodate
themselves to the new geometry without buckling, the shape of the
plastics composite thereby obtained being defined on at least said
first side by the plastic flow of the metal sheet.
2. A method according to claim 1, in which the thermoformable
material is thermoplastic.
3. A method according to claim 1, in which the thermoformable
material is thermosettable.
4. A method according to claim 1, in which the body of composite
comprises a sheet of thickness from 0.25 mm to 25 mm.
5. A method according to claim 1, in which the body of composite
comprises a pre-formed consolidated plastics sheet containing said
superimposed layers of fibres and the composite sheet is curved
about at least one axis in the plane of the composite sheet when
the metal sheet is urged against the body.
6. A method according to claim 1, in which the body of composite
comprises an assembly of prepreg sheets and the prepreg sheets are
consolidated together when the metal sheet is urged against the
body.
7. A method according to claim 1, in which the metal sheet is
superplastic.
8. A method according to claim 1, in which the body comprises a
plurality of separate pieces of said composite and the pieces are
joined together when the sheet is urged against the body.
9. A method according to claim 1, in which the metal sheet
comprises an inflatable diaphragm or parison.
10. A method according to claim 1, in which the body is positioned
directly between the metal sheet and a surface of said mould and
the metal sheet is deformed when urged against the body to press
the body against the mould surface.
11. A method according to claim 10, in which the mould surface is
provided with apertures, members to be attached to the body are
placed in the apertures and the members become attached to the body
when the body is pressed against the mould surface.
12. A method according to claim 1, in which the metal sheet has at
least one upstanding portion extending into or around the body when
the sheet is urged against the body, said upstanding portion
defining an edge of the shaped article extending in the direction
transverse to the sheet.
13. A method according to claim 12, in which the body is positioned
between said metal sheet and another deformable sheet which has an
aperture opposite said upstanding portion, the upstanding portion
entering the aperture when said metal sheet is urged against the
body.
14. A method according to claim 1, in which a lubricant is applied
between the surface of the metal sheet and the body.
15. A method according to claim 1, in which a layer of material is
interposed between the metal sheet and the body and said material
becomes adhered to the shaped article on urging of the sheet
against the body.
16. A method according to claim 1, in which an adhesive is applied
between the surface of the metal sheet and the body and the sheet
is adhered to the body when urged against the body.
17. A method according to claim 1, in which at least one member to
be attached to the body is positioned in contact with the body and
becomes attached to the body on plastic deformation of the sheet to
shape the body.
18. A method of forming a shaped article of a plastics composite
comprising fibers dispersed in a matrix of a thermoformable
material, comprising the steps of
providing a body of said composite to be reshaped and having a
first side and a second side;
confining both said first and second sides of said body of said
composite between sheets of metal which are capable of being
plastically deformed at an elevated temperature;
restraining the edges of said metal sheets;
bringing said metal sheets and the body to an elevated temperature
at which the metal sheets can be plastically deformed and at which
the body can conform to the shape of the metal sheets;
applying fluid pressure to one of the metal sheets at such a
pressure so that the metal sheets are plastically stretched
relative to the restrained edges and the body is formed to shape
between the stretched metal sheets, the shape of the plastics
composite thereby obtained being defined by the plastic flow of the
metal sheets; and
separating the stretched metal sheets from the resultant shaped
article.
19. A method according to claim 18, in which one of said sheet is
perforate to allow gases trapped between the sheets to escape.
20. A method according to claim 18, in which the space between said
metal sheets is evacuated to remove gases between the sheets.
21. A method according to claim 20, in which the peripheries of the
sheets are joined by a rigid gas-tight frame to form an enclosure
surrounding the body, the frame having an aperture and means for
creating a vacuum in the enclosure are connected to the aperture, a
vacuum is established in the enclosure and said metal sheet is
urged against the body while the vacuum is maintained in the
enclosure.
22. A method according to claim 21, in which after deformation of
the sheets and body the vacuum in the enclosure is maintained while
the body is allowed to cool.
Description
BACKGROUND OF INVENTION
This invention relates to methods of forming of shaped articles of
plastics composites comprising fibres dispersed in a matrix of a
plastics material.
Composite materials consisting of plastics reinforced by continuous
fibres, such as carbon and boron fibres, may be used for making
articles having a high strength to weight ratio and desirable
properties of stiffness and endurance. Articles made from such
composites are increasingly used in the aerospace industry. One
type of composite comprises fibres dispersed in a thermoplastic
material such as a polyaromatic polyether ether ketone, known as
PEEK available from Imperial Chemical Industries plc under the
Victrex trade mark. Another type of composite comprises
fibre-reinforced thermosetting materials and these are widely used
in aerospace and other industries. Composites containing
thermoplastic materials have the advantage over composites
containing thermosetting plastics that solidification of the
plastics material is reversible and a body of the solid composite
may be deformed to a desired shape by heating the composite to a
temperature at which the plastics material is deformable, followed
by forming to shape and cooling. This operation may be repeated and
allows articles made of the composite to be repaired; alternatively
the composite material can be recycled.
The extent to which a body of fibre/plastics composite may be
deformed when hot depends essentially on the arrangement of fibres,
which are generally inextensible, in the body. The composites are
commonly made as sheets in the form of superposed layers of
continuous fibres, in which the fibres of a layer may be woven
together and the fibres are impregnated so that individual
filaments of the fibre are surrounded and contacted by the plastics
material. When the sheet is deformed by bending and/or stretching
when hot, the plastics material flows to acquire the new shape of
the sheet, but it is also necessary for the structures formed by
the fibres to adapt themselves to the new shape. Imperfect
adaptation by the fibres can lead to faults of shape and/or
unsatisfactory mechanical properties in the shaped article. Some
conventional methods of forming cause "buckling" of the fibres
which are in compression after deformation, generally on the
concave side of a bend; also movement of one layer of fibre
relative to the next may produce delamination.
In the case of fibre/thermosettable polymer composites the problem
of producing shaped articles containing continuous fibres is less
of a problem when the thermosettable polymer is a low viscosity
curable resin, because the resin impregnated fibres are flexible
and nonrigid intermediate products which can be accommodated in
shaped moulds more readily. These systems do however suffer from
the disadvantage that long curing cycles are necessary so that the
productivity from the moulding equipment is low. The problem of
forming reinforced intermediate thermosettable products is however
very significant when the thermosettable polymer is not a low
viscosity resin but is of sufficiently high viscosity to confer
rigidity on the intermediate composite to be shaped and cured. This
is the case when the thermosettable material is a solid which has
been impregnated into the fibre structure by a solution process,
with the solvent subsequently being removed. Such products are
stiff, board-like materials which cannot be used in the manner of
the low viscosity resin/fibre composite materials to conform to the
shape of the mould. The present invention provides a method of
forming such board-like intermediate products. The method can also
be applied with advantage to the low viscosity resin/fibre
intermediate products.
SUMMARY OF INVENTION
According to one aspect of the invention there is provided a method
of forming a shaped article of a plastics composite comprising
fibres dispersed in a matrix of a thermoformable material in which
a body of said composite is contacted on at least one side of the
body by a sheet of a metal which is capable of being plastically
deformed at an elevated temperature, and the sheet is urged against
the side of the body whilst the sheet is at a temperature at which
it can be plastically deformed and the plastics body is at a
temperature at which it will conform to the shape of the sheet. The
sheet is preferably of a superplastic metal, such as a superplastic
aluminum alloy of the kind described in British Pat. Nos. 1387586
and 1445181.
The thermoformable material may be a thermoplastic or a
thermosettable material. In the case of a thermoplastic polymer
matrix, the thermoplastic should be at a temperature at which it is
plastically deformable. In the case of a thermosetting matrix which
has such a viscosity at ambient temperature such that the composite
body is a stiff rigid body, the temperature must be sufficient to
reduce the viscosity of the stiff thermosettable matrix to enable
the matrix to flow when subject to deformation applied through the
metal sheet. In the case of a fluid thermosettable resin matrix,
the body will already be readily deformable at ambient temperature.
In the latter case the invention gives advantages at the curing
stage.
Although any thermoplastics material may be used as the matrix, the
invention is of particular interest when the thermoplastics is an
aromatic polymer of high thermal stability such as poly aryl
ketones, polyamides, polyesters, polysulphones, polyethersulphones,
poly arylene sulphides, thermoplastic polyamides, polyetherimides
and polyamide-imides. The thermosetting materials include epoxy
resins and resins of higher thermal stability such as vinyl
polyester resins, polyimides, particularly those derived from
bismaleimides, phthalocyanine resins, polystyrylpyridines,
acetylene terminated imides and nadic terminated imides.
The method is particularly useful when applied to composite bodies
in the form of sheets having a thickness of 0.25 to 25 mm. The
length and width of the body will depend on the size of equipment
available for pressing or deforming. Sheets of dimensions 5
m.times.3 m can be handled in commercially available equipment.
Whilst the method is particularly useful for forming shaped
articles in which the fibres are continuous in the sense of
extending across the length or width of the sheet the method is
also useful when the fibres are present in shorter lengths for
example fibres having a length of at least 3 mm.
The method can be applied in a variety of ways and in some
embodiments shaping equipment of the kinds described in British
Pat. Nos. 1461317 and 1552826 may be used. In a first embodiment
the method can be applied to preferred, consolidated bodies such as
composite plastics sheets containing superimposed layers of
continuous, aligned fibres optionally woven so that a shaped
article is obtained from a substantially flat composite sheet by
deforming the sheet so that it has curvature about at least one
axis in the plane of the flat sheet. In this embodiment the
composite sheet may be urged into a female mould by pressure acting
on the metal sheet or urged over a male mould.
In a second embodiment the process can be used to form and
consolidate the body from thin prepreg sheets, whilst
simultaneously deforming the assembly of prepreg sheets into a
shaped article. The thin prepreg sheets in this embodiment may be
laid up prior to consolidation by superimposing prepreg sheets with
the fibre oriented in chosen directions so that the reinforcing
fibres provide quasi-isotropic reinforcement in the plane of the
sheet. Alternatively, strips of prepreg may be laid up in woven
fashion to provide one or more woven sheets to be consolidated.
Suitble prepreg materials and methods of producing such materials
are described in European Patent Publication No. 56703.
Thermosettable prepreg materials, particularly of the board-like
type, may also be used.
In a further embodiment the shaped article produced may be in the
form of a flat sheet which is produced by consolidating prepreg
materials, as described in the second embodiment of the invention.
Alternatively, in the case of thermoplastic products, the method
may be used to produce a flat sheet having an improved degree of
consolidation and surface finish from a preformed sheet which has
been consolidated between conventional metal platens which do not
plastically deform at elevated temperature. In this method a
plastically deformable metal sheet is used to urge and consolidate
the flat sheet against a rigid platen surface.
In all of these embodiments at least one sheet of plastically
deformable metal should be employed, the assembly of composite
sheet and metal sheet or sheets being termed a "sandwich". In the
case of the deformation of a preformed body of reinforced composite
to a shaped article having curvature a single sheet of metal may be
urged against the surface of the preformed body at appropriate
temperatures, contact between the metal sheet and the body being
maintained by appropriate pressure means. The preformed body may be
deformed into a female mould. It is possible to employ two
plastically deformable metal sheets, one on either side of the
body. When the other sheet is not metal it should be a material
which will conform to the shape conferred on the body by plastic
deformation of the metal sheet and should have a level of thermal
stability suitable for use at the elevated temperatures
employed.
When both sheets are of plastically deformable metal it is not
always necessary to deform the composite sandwich against a female
mould surface and useful shaped articles in the form of a freely
blown dome can be obtained.
When the method is used to form a shaped article having curvature
the composite body is supported by at least one metal sheet so that
buckling of the fibres is inhibited while the fibres are organised
to the new shape of the body. An accurately shaped composite body
may thus be obtained without loss of the desirable mechanical
properties of the composite.
The body of plastics composite may be a sheet having layers of
fibres arranged in the plane parallel to the metal sheet. The
sandwich may be deformed by stretching of the metal sheet, which
may if desired be superplastically deformable at the deformation
temperature used. The edges of the composite body are preferably
left free to move in the direction parallel to the sheet. As the
sandwich is deformed the fibres of the composite may then move to
accommodate themselves to the new shape of the body.
The invention is particularly useful for forming shaped articles of
non-uniform thickness which would be difficult or impossible to
consolidate or to deform using rigid flat platens or matched
moulds. The use of a plastically deformable metal sheet enables the
sheet to conform with and be urged against the irregular surface of
the body, the other surface being restrained by a rigid flat
surface or a male or female mould surface.
The shaping method according to the invention may be applied to a
flat body of composite material but it may also be applied to
bodies of composite material which already have a curvature. When
the body is to be formed to a complex shape, especially when it has
curvatures about more than one axis, the degree of deformation of
the sandwich, starting from a flat sandwich, may vary considerably
between different locations of the sandwich. If the sandwich has an
appropriate curvature initially the variation in deformation across
its area may be reduced substantially.
The shaping method may be applied to a single, continuous body of
composite material or to a body formed of thin sheets of composite
which are laminated together. It may also be applied to a composite
body which is initially built up of separate pieces of
fibre/plastics composite. The pieces may be cut and/or bent or
folded to make a body of the required initial shape by "Origami"
techniques. This method may be used, together with a mould of
appropriate shape, to form a composite body of more or less any
shape. For example, a tube of composite of circular, elliptical or
any other cross-section may be made by applying curved sheets of
the fibre/plastics composite material as a layer to the interior
surface of a tubular mould and providing the deformable sheet as an
inflatable gas-tight metal diaphragm or parison which fits into the
mould inside the composite layer. On application of heat to the
assembly thus formed and pneumatic pressure inside the parison the
latter expands with plastic deformation and presses the composite
material against the inside of the mould to form a tube.
When the composite body is made up of more than one piece the
pieces are consolidated together during deformation.
The method of the invention may also be used for joining to the
composite body members which are not themselves plastically
deformed or consolidated during urging of the sheet against the
body. For example, it may be desired to provide a surface of the
shaped composite body with upstanding brackets or webs having
flanges which are embedded in the composite body. Such members may
be accommodated in suitably shaped slots or grooves in the surface
of a mould to which the composite is applied and extend into the
composite body and become anchored within the body as the shaped
body is formed. The preconsolidated members may be placed in slots
in the mould surface and held therein by pressure exerted by a tool
as the shaped body is formed.
Under certain circumstances it may be desired to make shaped
articles of composite having edges of positively controlled shape
and position. This may be the case, for example, when the composite
is to be shaped into a curved sheet having holes of predetermined
location, size and shape. Such control may be exercised by
providing the surface of the deformable sheet with upstanding
portions which come into contact with the opposed surface of the
opposite deformable sheet, or the opposed surface of a mould
against which the composite is applied, so that the composite
cannot enter the area defined by the upstanding portions during the
deformation process. Instead of providing the upstanding portions
on the deformable sheet, they may be provided on the mould surface
instead when no deformable sheet separates the composite from the
mould surface. The upstanding portions may define holes in the
shaped composite body or they may define a peripheral outer edge of
the body. When the sandwich has deformable sheets on both sides of
the composite the upstanding portion of one sheet may extend
through a corresponding hole in the opposite sheet.
The temperature at which the sandwich is deformed depends on the
identity of the plastics materials used. In the case of
thermoplastic materials the temperature must be high enough to
allow the thermoplastic material to be deformed plastically and
give satisfactory bonding of the fibres after deformation. In the
case of PEEK, a deformation temperature from 340.degree. C. to
420.degree. C. may be used. However it may be possible to deform
the sandwich at a temperature below the melting point of the
thermoplastic. With semi-crystalline thermoplastics such as PEEK
the lowest usable temperature is generally determined by the
recrystallization behaviour of the material.
The sandwich may be deformed by a fluid pressure differential such
as gas pressure, the application of mechanical pressure or by a
combination of these methods. When a pressure differential is
applied to one side of the sandwich having two metal sheets but not
the other the metal sheet remote from the pressure application may
be perforated to ensure that any gases trapped in the sandwich are
released.
Alternatively, the space between the two sheets can be evacuated to
remove gases. In addition, if the vacuum (the word vacuum as used
herein is any reduced pressure below ambient pressure) between the
two sheets is sustained whilst the sandwich is being deformed, this
will maintain a consolidating force upon the plastics/fibre
composite additional to any consolidating force resulting from the
stretching of the metallic sheet. After deformation, in the case of
thermoplastics materials the sandwich is allowed to cool so that
the deformed composite body is "fixed" in shape. In the case of
thermosettable materials the sandwich will normally require to be
maintained at an elevated temperature, after the deformation
operation, to effect a complete cure of the resin. Application of
the pressure used in deformation may be continued after deformation
and during at least the first stage of cooling or curing so that
the body is retained under pressure as it cools in order to avoid
possible delamination of the composite body during cooling.
Cooling of the composite body after shaping may take place while
the body is still within a mould or press in which it has been
deformed to shape; alternatively the body, still in contact with
the deformable sheet or sheets, may be removed from the mould or
press while still hot so that it may cool at a faster rate. It is
then possible to control the rate of cooling of the shaped
composite by controlling the temperature of its surrounding
environment and such controlled cooling may be used to control the
mechanical properties of the composite body obtained. These
properties may, for example, depend on the relative proportions of
crystalline and amorphous species in the plastics material and
cooling at a controlled rate may allow these proportions to be
controlled.
In one possible method of forming the shaped article the composite
material to be shaped is placed between the two deformable sheets
which are joined at their peripheries by a rigid gas-tight frame so
that the frame and sheets form a gas-tight enclosure. The frame is
provided with one or more apertures connected by an umbilical to a
source of vacuum and the sheets with the composite between are
deformed in a press or mould while a vacuum is maintained between
the sheets. After shaping the enclosure is removed from the press
or mould and allowed to cool while the vacuum in the enclosure is
maintained. The vacuum then exerts a consolidating effect during
both the shaping and the cooling steps.
During deformation of the sandwich there is generally a degree of
slip between the composite body and the metal sheets and a
lubricant may be applied to the inside sheet surfaces to facilitate
slip.
After cooling of the sandwich the sheets may be removed to obtain
the shaped article of fibre-plastics coposite and before assembly
of the sandwich a release agent may be applied to the inside
surfaces of the metal sheets to facilitate removal. However the
method of the invention may be applied to fabrication of shaped
fibre-plastics bodies which are bonded on one or both sides to
metal sheets and in this case one or both sheets are retained
attached to the body after cooling. An adhesive, and not a release
agent, may then be applied to the appropriate metal sheet on
assembly of the sandwich to bond the shaped body firmly to the
plate.
The plastics composite to be formed to shape may be in direct
contact with the plastically deformable sheet or sheets during
deformation or it may be separated therefrom by a further layer of
material which is deformed together with the composite and
deformable sheet. This further layer may become permanently
attached to the plastics composite before or during deformation. It
may for example comprise an unfilled polymer film for improving the
surface finish of the shaped article or for other purposes. It is
also possible to incorporate a sheet or film of unfilled plastics
material within the body of composite material.
A particular advantage of the use of the invention with
thermosettable materials is that the deformable metal skin or skins
provides a rigidifying support which can retain the shape of the
deformed body even though the thermosettable material is not
completely cured. This is of particular advantage with the low
viscosity resin systems because it provides a means of reducing the
time during which the shaped article needs to be kept in the mould,
thus improving equipment utilisation. Thus final cure of the shaped
article can take place on the rigidifying metal support in an oven
at an appropriate temperature. Methods of forming a shaped body of
fibre-plastics composite will be described by way of example with
reference to the accompanying drawings.
DESCRIPTION OF DRAWINGS
FIG. 1 shows a sandwich comprising a sheet of fibre-thermoplastics
composite between two metal sheets,
FIG. 2 shows schematically a method of deforming the sandwich of
FIG. 1,
FIG. 3 shows schematically a method of deforming similar to that of
FIG. 1,
FIGS. 4 and 5 show schematically another method of deforming the
sheet of FIG. 1,
FIG. 6 shows a variant of the method of FIGS. 4 and 5,
FIG. 7 shows an article which may be obtained using the methods
described,
FIG. 8 shows schematically a method of making a tubular composite
article,
FIG. 9 shows schematically a method of making a composite article
having upstanding members.
FIGS. 10 and 11 show schematically another method of deforming a
sheet of composite material,
FIG. 12 shows yet another method of forming a composite material
sheet.
DESCRIPTION OF PARTICULAR EMBODIMENTS
Referring to FIG. 1, a sheet 1 of fibre-thermoplastics composite
sold by Imperial Chemical Industries plc under the designation
APC-1 and comprising layers of carbon fibre bonded in a matrix of
polyaromatic polyether ether ketone is sandwiched between sheets 2
and 3 of "Supral" superplastic aluminum alloy. Sheets 2 and 3
extend beyond the edges of sheet 1 and a coating of lubricant is
applied between sheet 1 and the inner surfaces of sheets 2 and 3. A
coating of adhesive or parting agent, as required, is also applied
between sheet 1 and these inner surfaces. The edges of the metal
sheets 2 and 3 extend beyond the edge of sheet 1 and the edges of
the latter are free from constraint.
For deformation the sandwich is put in contact with a forming tool,
heated to a temperature above 340.degree. C., and deformed. One
type of forming tool is shown schematically in FIG. 2. Using this
tool, the planar heated sandwich is positioned on female mould 4
and its edges are clamped, by conventional clamping means, against
the edges 5 of the mould. Fluid pressure, such as air pressure, is
then applied in the direction shown by arrows so that the sandwich
is deformed against the mould to take the shape shown in continuous
lines.
Sheet 2 adjacent the mould surface may be perforated to allow
escape of gases present in sheet 1 and the mould may be provided
with vents (not shown) to allow escape of gases from the space
between sheet 2 and the female mould surface. Alternatively the
space between unperforated sheets 2 and 3 may be evacuated. The air
pressure is maintained until the sandwich has cooled sufficiently
to avoid delamination.
The mould may take a variety of shapes for moulding differently
shaped articles. One shape of mould allowing re-entrant curves to
be produced is shown in FIG. 3. Deformation with this mould is
carried out in the same way as in the mould of FIG. 2.
Another method of deformation is shown schematically by FIGS. 4 and
5. In this case the sandwich, heated to above 340.degree. C.,
clamped at its edges 6, is deformed by mechanical force applied to
the "plug" tool 7 so that the sandwich is deformed as shown in FIG.
4. Air pressure is then applied to the reverse surface of the
sandwich as shown by arrows in FIG. 5 so that the sandwich is
further deformed and assumes the shape defined by the plug. In this
embodiment the metal sheet in contact with the plug may be
perforated to allow escape of gas. Alternatively the space between
unperforated sheets 2 and 3 may be evacuated. The plug tool remains
in place, and the air pressure is maintained, while the sandwich
cools to a temperature at which delamination will not occur.
The method shown in FIGS. 4 and 5 may be preceded by a "bubble
blowing" step as shown in FIG. 6, in which air pressure is first
applied to the surface of sheet 3 without any mould abutting sheet
2 and with the edges of the sandwich clamped. A male tool may then
be inserted in the "bubble" formed, as shown in FIG. 4, and air
pressure applied to sheet 2 as shown in FIG. 5. In this method the
sandwich is deformed entirely by air pressure and no deforming
force need be applied to the tool 7. As air pressure is applied to
both sides of the sandwich neither of the sheets 2 and 3 should be
perforated.
The operations described above may be carried out using shaping
equipment which is in current use for deforming metal sheets.
Instead of applying fluid pressure, the sandwich may be deformed by
forces applied using solid dies. A wide variety of shapes of
article may be produced, including articles having double
curvature, that is curvature about two or more axes in the plane of
the original flat sheet which are transverse to each other.
The methods described may be used for making shaped articles of
composite which are attached on both, one or neither side to the
metal sheets used in the deformation process. The methods described
may be used for making articles from metal sheet adhered to the
body of composite on only part of their surface. One such article
is shown by way of example in FIG. 7. This article comprises the
metal sheets, deformed as described above, with a patch 10 and a
strip 11 of the composite material adhered to parts of their inside
surfaces. This article may be made by the methods described above,
using a sandwich in which only parts of the sheets 2 and 3 are
separated by sheet 1.
FIG. 8 shows a method of making a tubular shaped body of
fibre/plastics composite. A tubular mould 12, comprising a pair of
half-moulds clamped together at 13 in known manner, is assembled
and pieces of fibre/plastics pre-preg sheet are placed inside the
mould to form a layer 14 adjacent its inside surface. The pieces of
pre-preg sheet may be assembled together by known techniques such
as circular braiding or use of part-circles. An inflatable,
plastically deformable metal parison 15 is then inserted within the
layer 14 and the assembly is heated to the temperature required for
plastic deformation of the parison and pre-preg layer which
pneumatic pressure is inserted within the parison to press the
layer 14 against the mould wall. When layer 14 has consolidated
into a firm tube the temperature of the assembly is lowered, the
parison deflated and removed and the mould is opened to allow
release of the tube. The mould 12 may be of circular, elliptical or
any other cross-section depending on the desired cross-section of
the composite tube.
FIG. 9 illustrates a method of incorporating upstanding members, in
this case brackets, in a surface of the composite body. The
brackets are composed of the same material as the composite body. A
mould is in three parts 16, 17 and 18 separated by gaps 19 in which
the upstanding arms of brackets 20 of fibre/plastics composite
sheet are inserted. A layer 21 of fibre/plastics composite is
deposited on the mould surface, surrounding the parts of the
brackets extending above the surface, and a sheet 22 of "Supral"
alloy is placed in contact with the composite. On application of
heat and pressure to the alloy sheet the composite material layer
21 is deformed and consolidated while parts 16 and 18 of the mould
are pressed against part 17, compressing arms 20 of the brackets.
On release of pressure from the sheet 21 the mould parts are
separated from each other to release arms 20 from the mould.
The method shown in FIGS. 10 and 11 is the same as that shown in
FIG. 6. However in this method the sheet 3 is provided with outer
and inner upstanding portions 31, 32 and sheet 2 is provided with
holes or indents 33,34 opposite the upstanding portions. The
upstanding portions are dimensioned to fit into the holes or
indents when sheets 2 and 3 are brought together. As shown in FIG.
10, a layer of fibre-plastics composite is disposed between the
sheets such that, on pressing, the outer upstanding portions 31 are
located outside the composite layer by a short distance and the
inner upstanding portion 32 defines a hole in the composite sheet.
When deforming pressure is exerted on sheet 2, as shown in FIG. 11,
the sheets 2 and 3 move together and the upstanding portions of
sheet 3 enter the apertures of sheet 2. During this operation the
layer 1, being under compression, is urged against the sides of the
upstanding portions which consequently define edges of the shaped
sheet of composite. The outer portions 31 define an outer edge of
the sheet 1 and the inner portion 32 defines a hole in the sheet
1.
Using this method, by providing suitably arranged upstanding
portions a sheet having any number of holes of any desired shape
may be made and the sheet may have any desired peripheral shape,
defined by outer portions 31. The outer upstanding portions may
form a continuous barrier around the edge of sheet 1 to define the
entire periphery of the sheet.
In a method similar to that of FIGS. 10 and 11, sheet 3 has
equivalent upstanding portions but sheet 2 has a continuous surface
which has no apertures. In this instance the upstanding portions
abut the surface of sheet 2 without penetrating it and define the
shape of the formed sheet in the same way as in the variant of
FIGS. 10 and 11. This variant is applicable to sandwiches
comprising only one sheet, in which case the upstanding portions on
sheet 3 abut the surface of a mould instead of sheet 2.
FIG. 12 shows a method of forming the composite article in which
the composite material is subjected to a vacuum during deformation
to remove trapped gases. In this method a sandwich comprising
composite layer 1 and sheets 2 and 3 is assembled as in FIG. 1, and
is surrounded by a rigid gas-tight frame 41 engaging sheets 2 and 3
around their whole periphery to form a gas-tight enclosure. Frame
41 has at least one aperture 42 in communication with an end of
umbilical tube 43. The other end of tube 43 is connected to a
vacuum pump of known type (not shown in the drawing). After
assembly as shown in FIG. 12 the enclosure is evacuated through
tube 43 and the assembly is heated to the deformation temperature,
and deformed by pressure applied to sheet 2, while the vacuum
within the enclosure is maintained to remove gases present between
sheets 2 and 3. The assembly may then be allowed to cool, the
vacuum released and frame 41 removed.
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